Trouble with crumb structure on high hydration sourdough loaf

So I've only recently been experimenting with high hydration loaves, and have had mostly good results. The loaf I baked last night, however, was not the best. It definitely lacked on oven spring, and the crumb was way too closed and spongy. I didn't write everything down this time, but so far as I remember I made the leaven at about 1 AM, which was 50 G starter, 150 G all purp flour (heartland mills), and 150 gram king arthur whole wheat. When I checked it at 10:30 AM the leaven was active and floated in water. I made enough dough for two fairly large boules by mixing 1150 grams of flour ( a mixture of all purpose flour, bread flour, whole wheat, and a little coarse rye,) and 850 grams water, coming out to about a 74 percent hydration, not including the leaven...which I used 220 grams of. I let the dough bulk ferment while stretching and folding during the first few hours for seven hours total, then I let one loaf (the one the in picture,) rise at room temperature for 3 and a half hours and baked it that night, the other loaf proofed in the refridgerator for about 18 hours and was immediately thrown in the oven....it looks slightly better, but probably isn't a whole lot better. Any suggestions? I'm thinking this may have overproofed...causing the tight crumb structure, or just not enough practice shaping wet dough...